Microelectromechanical gyroscope and method for compensating an output thermal drift in a microelectromechanical gyroscope

ABSTRACT

A microelectromechanical gyroscope includes: the support structure; a sensing mass, coupled to the support structure with degrees of freedom along a driving direction and a sensing direction perpendicular to each other; and a calibration structure facing the sensing mass and separated from the sensing mass by a gap having an average width, the calibration structure being movable with respect to the sensing mass so that displacements of the calibration structure cause variations in the average width of the gap. A calibration actuator controls a relative position of the calibration structure with respect to the sensing mass and the average width of the gap.

BACKGROUND Technical Field

The present disclosure relates to a microelectromechanical gyroscope andto a method for compensating an output thermal drift in amicroelectromechanical gyroscope.

Description of the Related Art

As is known, in microelectromechanical gyroscopes the stability of thezero rate output (ZRO) is a key parameter for the quality of performanceand may be critical for very high accuracy.

The quadrature error is one of the dominant factors that determine theextent of the zero rate output (ZRO) in microelectromechanicalgyroscopes. In short, the quadrature error is caused by imperfectionsthat affect the output signals. Simplifying, a microelectromechanicalgyroscope comprises a driving mass, constrained to a support structureto oscillate with (at least) one degree of freedom according to adriving direction, and a sensing mass, constrained to the driving massto be dragged along the driving direction and to oscillate with respectto the driving mass with (at least) one degree of freedom according to asensing direction, perpendicular to the driving direction. When thesupport structure rotates around a rotation axis perpendicular to thedriving direction and to the sensing direction, the sensing mass issubject to a fictitious force in the sensing direction, dependent on theangular velocity and on the speed in the driving direction, due todragging. The displacement of the sensing mass caused by the fictitiousforce is transduced into an electrical signal proportional to theangular velocity with respect to the rotation axis. According to otherknown solutions, a single movable mass is constrained to the supportstructure and may oscillate with a degree of freedom along the drivingdirection and with a degree of freedom along the sensing direction.Therefore, the mass acts as a driving mass and a sensing mass at thesame time.

Due to unavoidable defects associated with the manufacturing of theconnection elements between the support structure and the movable massor movable masses, the driving direction is not perfectly perpendicularto the sensing direction. The result is a displacement in the sensingdirection which is caused by the same driving motion and results in aquadrature noise signal component, which is phase-shifted by 90° withrespect to the useful signal. This component is present even when thegyroscope is at rest and gives rise to an offset in the output signal.The amplitude and stability of the offset during the lifespan are keyparameters for the new generation gyroscopes.

The quadrature error is also one of the factors that most affects thestability of the zero rate output, through dependence of the phase onthe temperature.

In order to reduce the drift of the zero rate output, it is known toadopt some measures, which are not entirely satisfactory for severalreasons.

A first known solution is the so-called family compensation. Inpractice, a same correction, determined on a statistical basis, isapplied to all the gyroscopes of a family. The correction is carried outin a digital manner on the output, based on the quadrature estimated forthe family and on the measured temperature. Although interesting becauseit is inexpensive, the solution is nevertheless not particularlyaccurate precisely because it is not individualized. Accordingly,devices whose parameters depart from the parameters of the devices usedas a basis to determine the family compensation show a residual drift ofthe output.

A more accurate solution is the individual calibration of thegyroscopes, whereby a specific correction is determined and digitallyapplied for each device. The accuracy of the calibration is obviouslyhigher, but the procedure is expensive and takes extremely long time.

According to a further known solution, a closed-loop dynamiccompensation is carried out. The gyroscopes are provided with electrodesand sense circuits configured to sense the actual offset eithercontinuously or by samples and with closed-loop compensation circuitsthat determine and apply a compensation signal to the output signalaccording to the sensed offset. The solution may be very accurate, it iscapable of adapting the compensation to the actual conditions of thegyroscope and is also effective for the drifts that occur during thelifespan of the device. However, the used compensation circuits have acomplex architecture and, in addition to being expensive in terms ofproduction costs, are also expensive in terms of energy consumption,which is another fundamental parameter.

BRIEF SUMMARY

The present disclosure is directed to providing a microelectromechanicalgyroscope and a method for compensating an output thermal drift in amicroelectromechanical gyroscope which allow the described abovelimitations to be overcome or at least mitigated.

According to the present disclosure a microelectromechanical gyroscopeand a method for compensating an output thermal drift in amicroelectromechanical gyroscope.

In at least one embodiment, a microelectromechanical gyroscope includesa support structure. A sensing mass, coupled to the support structurewith degrees of freedom along a driving direction and a sensingdirection, the driving direction and the sensing direction aretransverse to or perpendicular to each other. A calibration structurefacing the sensing mass and separated from the sensing mass by a gaphaving an average width, the calibration structure being movable withrespect to the sensing mass so that displacements of the calibrationstructure cause variations in the average width of the gap. Acalibration actuator configured to control a relative position of thecalibration structure with respect to the sensing mass and the averagewidth of the gap.

In at least one embodiment, a method includes compensating an outputthermal drift in a microelectromechanical gyroscope, including:arranging a calibration structure of the microelectromechanicalgyroscope facing the sensing mass and separated from the sensing mass bya gap having an average width, and moving the calibration structure tovary the average width of the gap.

In at least one embodiment, a system includes a microelectromechanicalgyroscope including: a support structure having a surface; a cap coupledto the support structure; a chamber delimited by the support structureand the cap; an anchor extending from the support structure into thechamber; a sensing mass coupled to the support structure by a pluralityof flexures and overlying the surface of the support structure; afulcrum coupled to an end of the anchor spaced apart from the surface ofthe support structure, the fulcrum having a fulcrum axis; a calibrationstructure coupled to the fulcrum, the calibration structure having: acalibration plate coupled to the fulcrum, the calibration plate having afirst portion on a first side of the fulcrum axis and a second portionon a second side of the fulcrum axis, the first portion overlapping thesensing mass; a gap extending from the calibration plate to the to thesensing mass. A processing unit coupled to the microelectromechanicalgyroscope.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the disclosure, some embodiments thereofwill now be described, purely by way of non-limiting example and withreference to the attached drawings, wherein:

FIG. 1 is a cross-section through a microelectromechanical gyroscope inaccordance with an embodiment of the present disclosure;

FIG. 2 is a top plan view of the microelectromechanical gyroscope ofFIG. 1 , cut along line II-II of FIG. 1 ;

FIG. 3 is a simplified block diagram of the microelectromechanicalgyroscope of FIG. 1 ;

FIGS. 4 and 5 are graphs that show quantities relating to families ofgyroscopes before and after a family calibration operation,respectively;

FIGS. 6 and 7 show the microelectromechanical gyroscope of FIG. 1 in afirst operating configuration and in a second operating configuration,respectively;

FIGS. 8-13 are cross-sections through a semiconductor wafer insuccessive steps of a manufacturing process of themicroelectromechanical gyroscope of FIG. 1 ;

FIG. 14 is a top plan view, with parts removed for sake of clarity, of amicroelectromechanical gyroscope in accordance with a differentembodiment of the present disclosure;

FIG. 15 is a front view of the microelectromechanical gyroscope of FIG.14 , cut along line XV-XV of FIG. 14 ;

FIG. 16 is a top plan view, with parts removed for sake of clarity, of amicroelectromechanical gyroscope in accordance with a further embodimentof the present disclosure;

FIG. 17 is a front view of the microelectromechanical gyroscope of FIG.16 , cut along line XVII-XVII of FIG. 16 ; and

FIG. 18 is a simplified block diagram of an electronic systemincorporating a microelectromechanical gyroscope according to thepresent disclosure.

DETAILED DESCRIPTION

With reference to FIG. 1 , a microelectromechanical gyroscope inaccordance with an embodiment of the present disclosure is schematicallyillustrated and indicated with the number 1 and comprises a packagingstructure 2, a movable sensing mass 3 and a calibration structure 5.

The packaging structure 2 comprises a support structure 6 and a cap 7joined together in a gas-tight manner and defining a hermetically closedand sealed chamber 8 between each other. A controlled atmosphere, forexample low-pressure argon, is present in the chamber 8. The supportstructure 6 may be a single monolithic semiconductor body or includeseveral layers, for example a monocrystalline substrate and one or moreepitaxial layers connected to each other and to the substrate directlyor through intermediate layers, such as dielectric, for example ofsilicon oxide, or conductive layers, such as layers of suitably dopedpolycrystalline silicon.

The sensing mass 3 and the calibration structure 5 are accommodated inthe chamber 8. The support structure 6 and the cap 7 delimit the chamber8, which may be referred to as a cavity.

The sensing mass 3 is of semiconductor material, for examplemonocrystalline epitaxial silicon, and is constrained to the supportstructure 6 through flexures 10. The flexures 10 are configured to allowthe sensing mass 3 to oscillate with respect to the support structure 6along a driving direction DD, parallel to a face 6 a, which may bereferred to as a surface, of the support structure 6, and along asensing direction DS, transverse to or perpendicular to the face 6 a andto the driving direction DD. Driving actuators 12 are operable to causethe sensing mass 3 to oscillate along the driving direction DD withcontrolled frequency and amplitude. For example, the driving actuators12 may comprise electrode groups fixed to the support structure 6 andmovable electrode groups fixed to the sensing mass 3, coupled incomb-fingered configuration.

The sensing mass 3, made conductive through doping, is capacitivelycoupled to a sensing electrode 13 arranged on the face 6 a of thesupport structure 6 and facing the sensing mass 3.

The calibration structure 5 is connected to a fulcrum 15 fixed to thesupport structure 6 through an anchor 16 and may rotate around a fulcrumaxis F parallel to the face 6 a and transverse to or perpendicular toboth the driving direction DD and the sensing direction DS. More indetail, the calibration structure 5 comprises a calibration plate 17 anda coupling mass 18 capacitively coupled to a calibration electrode 20 onthe face 6 a of the support structure 6. The calibration plate 17 andthe coupling mass 18 are joined together to form a single rigid body.The fulcrum 15 is at an end of the anchor that is spaced apart from theface 6 a of the support structure 6.

The calibration plate 17 is connected to the fulcrum 15 and has a firstportion 17 a and a second portion 17 b opposite with respect to thefulcrum 15. In one embodiment, the calibration plate 17 is off-centerwith respect to the fulcrum 15, in such a way that the first portion 17a has a greater size than the second portion 17 b. The first portion 17a faces the sensing mass 3 on the side opposite to the support structure6 and is separated from the sensing mass 3 by a gap 21. The sensing mass3 is therefore located between the sensing electrode 13 and thecalibration structure 5 along the sensing direction DS. The averagewidth W of the gap 21 is determined by the rest position of the sensingmass 3 and by the position of the calibration structure 5 as explainedin detail hereinafter. The first portion 17 a is on a first side of thefulcrum axis F and the second portion is on a second side of the fulcrumaxis F when the calibration plate 17 is in the position as shown in FIG.1 .

The coupling mass 18 is capacitively coupled to the calibrationelectrode 20 and is therefore subject to an electrostatic force havingsign and intensity dependent on the bias of the calibration electrode20.

The gyroscope 1 is provided with a control unit 25, schematicallyillustrated in FIG. 3 , which, inter alia, has the task of determiningthe bias of the calibration electrode 20. The control unit 25 comprisesa driving device 26, configured to cause the sensing mass 3 to oscillatealong the driving direction DD with controlled frequency and amplitude,a sensing device 27, configured to sense the displacements of thesensing mass 3, which is a movable mass, along the sensing direction DSand to convert the sensed displacements into an output signal SOindicative of the rotation speed of the gyroscope 1, a calibrationmodule 28 and a charge pump 30. The calibration module 28 drives thecharge pump 30, which is coupled to the calibration electrode 20 andsets a calibration voltage VC. In practice, therefore, the calibrationelectrode 20 and the charge pump 30 define a calibration actuatorconfigured to control the relative position of the calibration structure5 with respect to the sensing mass 3 and, in particular, the averagewidth W of the gap 21.

The compensation of the drift of the zero rate output of the gyroscope 1due to the temperature occurs in the following manner. Initially, afamily calibration, which in one embodiment is carried out by thecalibration module 28 by acting on the sensing device 27 to modify theoutput signal SO, is applied. The family calibration is determined on astatistical basis by the observation of a sample of gyroscopes havingidentical structure to the gyroscope 1. An average error is determinedfrom a distribution of the drift of the zero rate output of the sample(FIG. 4 ) and a corresponding correction is applied to all thegyroscopes of the family. The effect of the family calibration isillustrated in FIG. 5 . The residual difference in temperature drift isdue to the spread of the quality factor Q, which due to processimperfections varies from device to device. The quality factor Q isinfluenced by the mobility of gas molecules in the chamber 8, which, inturn, depends on the distance from surrounding masses. In the gyroscope1, in particular, the quality factor Q is proportional to the squareroot of the average width W of the gap 21 between the sensing mass 3 andthe first portion 17 a of the calibration plate 17, that is of theportion of the calibration structure 5 facing the sensing mass 3 itself:

$Q \propto \sqrt{W}$

By acting on the calibration electrode 20, the electrostatic forceapplied to the calibration structure 5 may be modulated through thecoupling mass 18 and therefore the amplitude of the gap 21 may be variedby modifying the quality factor Q accordingly to cancel or, in any case,substantially reduce the temperature drift of the output signal SO inabsence of rotation, that is the zero rate output (ZRO). In particular,in the embodiment of FIG. 1 the modulation of the electrostatic forcethrough the calibration electrode 20 allows the calibration structure 5to be rotated counterclockwise, which may be referred to as a firstrotation direction, to reduce the width W of the gap 21 and the qualityfactor Q and clockwise, which may be referred to as a second rotationdirection that is opposite to the first rotation direction, to increasethe width W of the gap 21 and the quality factor Q. The correction ofthe quality factor Q is extremely simple and quick to perform and maytherefore be performed on each individual device without spending toomuch time to substantially cancel the offset on the output signal SOcaused by the quadrature error. The control unit 25 may itself beprovided with a calibration function, for example activatable on commandor when certain stability conditions occur. In this manner, thecalibration of the zero rate output may be carried out not only in thefactory before use, but also subsequently during the lifespan of thedevice to eliminate components that may arise with aging,thermo-mechanical stress and, in general, environmental factors.

FIG. 6 shows the microelectromechanical gyroscope 1 of FIG. 1 in a firstoperating configuration. As shown in FIG. 6 , the calibration plate 17is in a first position when the microelectromechanical gyroscope 1 is inthe first operating configuration. When in the first operatingconfiguration, the calibration plate 17 has rotated in acounterclockwise direction such that the first portion 17 a has rotatedtowards the sensing mass 3 and the second portion 17 b has rotated awayfrom the calibration electrode 20. When the calibration plate 17 is inthe first position, the average width W decreases such that the averagewidth W as shown in FIG. 6 is less than the average width W as shown inFIG. 1 .

FIG. 7 shows the microelectromechanical gyroscope 1 of FIG. 1 in asecond operating configuration different from the first operatingconfiguration as shown in FIG. 6 . As shown in FIG. 7 , the calibrationplate 17 is in a second position when the microelectromechanicalgyroscope 1 is in the second operating configuration. When in the secondoperating configuration, the calibration plate 17 has rotated in theclockwise direction such that the first portion 17 a has rotated awayfrom the sensing mass 3 and the second portion 17 b has rotated towardthe calibration electrode 20. When the calibration plate 17 is in thesecond position, the average width W increases such that the averagewidth W as shown in FIG. 7 is greater than the average width W as shownin FIG. 1 .

As should be readily appreciated, the first position of the calibrationplate 17 is different from the second position of the calibration plate.When the calibration plate 17 is in the first position as shown in FIG.6 , the first portion 17 a of the calibration plate 17 is closer to thesensing mass 3 as compared to when the calibration plate 17 is in thesecond position as shown in FIG. 7 . When the calibration plate 17 is inthe first position, the second portion 17 b of the calibration plate 17is further away from the calibration electrode 20 as compared to whenthe calibration plate 17 is in the second position as shown in FIG. 7 .

The gyroscope 1 of FIG. 1 may be formed through the process hereinafterdescribed with reference to FIGS. 8-16 . In practice, the sensing mass3, the coupling mass 18 and the anchor 16 of the fulcrum 15 on one sideand the calibration plate 17 on the other are obtained from twostructural layers epitaxially grown one on the other, as described indetail hereinafter.

With reference to FIG. 8 , a first dielectric layer 51, for example ofsilicon oxide, is grown on a substrate 6′ of a wafer 50 of semiconductormaterial, for example monocrystalline silicon. A conductive layer (notshown), for example of polycrystalline silicon, is deposited on thefirst dielectric layer 51 and shaped to form the sensing electrode 13and the calibration electrode 20. A first sacrificial layer 53, forexample of thermally grown or deposited silicon oxide, is formed on thefirst dielectric layer 51, above the sensing electrode 13 and thecalibration electrode 20. The first sacrificial layer 53 is selectivelyetched in positions corresponding to the anchor 16 and to perimeter(peripheral) portions of the support structure 6, which will be formedlater. Then, a first epitaxial layer 55 is formed above the firstsacrificial layer 53. The first epitaxial layer 55 has a thickness whichis determined on the basis of the characteristics of the desiredmicro-electro-mechanical structures and may be comprised, for example,between 2 and 80 μm. After the epitaxial growth, the first epitaxiallayer 55 is planarized and brought to the desired final thickness, forexample through CMP (Chemical Mechanical Polishing).

The first epitaxial layer 55, FIG. 9 , is etched to define bottomportions of the desired structures and of other intended regions. Inparticular, in this step the driving actuators 12 and the flexures 10(not shown here) may be formed from the first epitaxial layer 55.Furthermore, portions of the first epitaxial layer 55 intended to formthe sensing mass 3, the coupling mass 18 and the anchor 16 are separatedfrom each other. To this end, the wafer 50 is covered by a resist mask(not shown), which may be referred to as a first trench mask, andsubject to a dry etching, forming trenches 61, which completely passthrough the first epitaxial layer 55. The etching stops automatically onthe first sacrificial layer 53.

Then, a second sacrificial layer 60, for example of TEOS (TetraEthylOrthoSilicate), is deposited for a thickness comprised, for example,between 1 and 2 μm. The second sacrificial layer 60 partially fills thetrenches 61, for example for one third of their depth although thisfilling, as well as the filling extent and depth are not important. Thesecond sacrificial layer 60 is then planarized.

The second sacrificial layer 60 is selectively etched and removed, usinga masking layer (not shown), which may be referred to as a second anchormask to form openings 62, as illustrated in FIG. 10 . The etching of thesecond sacrificial layer 60 automatically terminates on the firstepitaxial layer 55. In general, the second anchor openings 62 are formedin the zones where forming connection regions between the firstepitaxial layer 55 and a second epitaxial layer which will be formedlater is desired. In particular, here, the second anchor openings 62 areformed in positions corresponding to the fulcrum 15, to a junction zonebetween the coupling mass 18 and the calibration plate 17 and toperimeter portions of the wafer 50.

Subsequently, FIG. 11 , a second epitaxial layer 65 is grown, for athickness also here linked to the desired micro-electro-mechanicalstructures, and which may be comprised also here between 2 and 80 μm. Ingeneral, the second epitaxial layer 65 may be thinner than the firstepitaxial layer 55, although the opposite may occur and the disclosureis not limited to any particular ratio between the thicknesses of theepitaxial layers 55, 65.

After the epitaxial growth, the second epitaxial layer 65 is planarizedand brought to the desired final thickness, for example through CMP(Chemical Mechanical Polishing). In this manner, the structural layerformed by the first and the second epitaxial layers 55, 65, alsoreferred to as overall epitaxial layer, reaches a final thickness,typically variable between 20 and 80 μm.

The wafer 50 is etched as shown in FIG. 12 . To this end, the wafer 50is covered by a resist mask (not shown) and subject to a dry etching. Inthis step, the portions of the epitaxial layers 55, 65 not covered bythe second trench mask are removed for the entire thickness of theoverall epitaxial layer and the etching stops on the first sacrificiallayer 53. In particular, in this step the sensing mass 3, thecalibration plate 17 and the coupling mass 18 are defined.

Then, FIG. 13 , the residual portions of the second sacrificial layer 60and the first sacrificial layer 53 are removed, releasing the movablemass and the calibration structure 5.

Finally, a cap wafer (not shown), which corresponds to the cap 7, isbonded to the wafer 50 through an adhesive layer and the composite waferthus obtained is diced to form the gyroscope 1 of FIG. 1 . The perimeterportions of the epitaxial layers 55, 65 in each die form, with therespective portion of the substrate 6′, the support structure 6 of thegyroscope 1.

With reference to FIGS. 14 and 15 , a microelectromechanical gyroscope100 in accordance with an embodiment of the present disclosure comprisesa packaging structure 102, a sensing mass 103 and a calibrationstructure 105. The packaging structure 102 comprises a support structure106 and a cap 107 joined together or coupled together in a gas-tightmanner and defining a hermetically closed chamber 108 between each otherwherein a controlled atmosphere, for example low-pressure argon, ispresent.

The sensing mass 103 and the calibration structure 105 are accommodatedin the chamber 108. The support structure 106 and the cap 107 delimitthe chamber 108, which may be referred to as a cavity.

The sensing mass 103, of semiconductor material, is frame-shaped and isconstrained to the support structure 106 through flexures 110. Theflexures 110 are configured to allow the sensing mass 103 to oscillatewith respect to the support structure 106 along a driving direction DD′and along a sensing direction DS′, both parallel to a face 106 a of thesupport structure 106, and transverse to or perpendicular to each other.Driving actuators 112 are operable to cause the sensing mass 103 tooscillate along the driving direction DD′ with controlled frequency andamplitude.

Sensing electrodes 113 fixed to the support structure 106 face and arecapacitively coupled to respective sides of the sensing mass 103. In oneembodiment, the sensing electrodes 113 are arranged inside the framestructure of the sensing mass 103.

The calibration structure 105 is defined by a mass 109 connected to thesupport structure 106 through flexures 115 which allow movements alongthe sensing direction DS′. The calibration structure 105 has a firstside 105 a facing one side of the sensing mass 103 and separated fromthe sensing mass 103 by a gap 121. The average width W′ of the gap 121is determined by the rest position of the sensing mass 103 and by theposition of the calibration structure 105. Furthermore, the calibrationstructure 105 is capacitively coupled to a calibration electrode 120arranged on the support structure 106 and facing a second side 105 b ofthe calibration structure 105 opposite to the first side 105 a. Thecalibration electrode 120 may be used in combination with the chargepump 30 of FIG. 3 to form a calibration actuator controlled by thecalibration module 28. The calibration structure 105 is thereforesubject to an electrostatic force of intensity dependent on the bias ofthe calibration electrode 120. By acting on the calibration electrode120, the electrostatic force applied to the calibration structure 105may be modulated and therefore the amplitude of the gap 121 may bemodified by modifying the quality factor Q accordingly to cancel or, inany case, substantially reduce the temperature drift of the zero rateoutput. In particular, in the embodiment of FIGS. 14 and 15 , thecalibration structure 105 may be moved closer to the sensing mass 103 toreduce the width W′ of the gap 121 and the quality factor Q and movedaway from the sensing mass 103 to reduce the width W′ of the gap 121 andthe quality factor Q.

With reference to FIGS. 16 and 17 , a microelectromechanical gyroscope200 in accordance with an embodiment of the present disclosure comprisesa packaging structure 202, a driving mass 201, a sensing mass 203 and acalibration structure 205. The packaging structure 202 comprises asupport structure 206 and a cap 207 joined together or coupled togetherin a gas-tight manner and defining a hermetically closed chamber 108between each other wherein a controlled atmosphere, for examplelow-pressure argon, is present.

The driving mass 201, the sensing mass 203 and the calibration structure205 are accommodated in the chamber 208. The support structure 206 andthe cap 207 delimit the chamber 208, which may be referred to as acavity.

The driving mass 201, of semiconductor material, is C-shaped and isconstrained to the support structure 206 through flexures 210 a. Theflexures 210 a are configured to allow the driving mass 201 to oscillatewith respect to the support structure 206 along a driving direction DD″parallel to a face 206 a of the support structure 206 itself. Drivingactuators 212 are operable to cause the driving mass 201 to oscillatealong the driving direction DD″ with controlled frequency and amplitude.

The sensing mass 203, also of semiconductor material, is accommodatedinside the driving mass 201 and faces the open side and is constrainedto the driving mass 201 through flexures 210 b. The flexures 210 b areconfigured to allow the sensing mass 203 to oscillate with respect tothe driving mass 201 and therefore with respect to the support structure206 along a sensing direction DS″, parallel to the face 206 a of thesupport structure 206 and transverse to or perpendicular to the drivingdirection DD″.

A sensing electrode 213 fixed to the support structure 206 faces and iscapacitively coupled to one side of the sensing mass 203. In oneembodiment, the sensing electrode 213 is arranged between the sensingmass 203 and the closed side of the C-shaped sensing mass 203.

The calibration structure 205 is defined by a mass 209 connected to thesupport structure 206 through flexures 215 which allow movements alongthe sensing direction D″. The calibration structure 205 has a first side205 a facing one side of the sensing mass 203 and separated from thesensing mass 203 by a gap 221. The average width W″ of the gap 221 isdetermined by the rest position of the driving mass 201 and by theposition of the calibration structure 205. Furthermore, the calibrationstructure 205 is capacitively coupled to a calibration electrode 220arranged on the support structure 206 and facing a second side 205 b ofthe calibration structure 205 opposite to the first side 205 a. Thecalibration electrode 220 may be used in combination with the chargepump 30 of FIG. 3 to form a calibration actuator controlled by thecalibration module 28. Also in this case, by acting on the calibrationelectrode 220, the amplitude of the gap 221 may be modified by modifyingthe quality factor Q accordingly to cancel or, in any case,substantially reduce the temperature drift of the zero rate output.

FIG. 18 shows an electronic system 300 which may be of any type, inparticular, but not limited to, a wearable device, such as a watch, asmart bracelet or band; a computer, such as a mainframe, a personalcomputer, a laptop or a tablet; a smartphone; a digital music player, adigital camera or any other device for processing, storing, transmittingor receiving information. The electronic system 300 may be a generalpurpose or device embedded processing system, an equipment or a furthersystem.

The electronic system 300 comprises a processing unit 302, memorydevices 303, a microelectromechanical gyroscope according to thedisclosure, for example the microelectromechanical gyroscope 1 of FIG. 1, and may also be provided with input/output (I/O) devices 305 (e.g., akeyboard, a pointer, a touch screen, or some other suitable type ofinput or interface device), a wireless interface 306, peripherals 307.1,. . . , 307.N and possibly further auxiliary devices, not shown here.The components of the electronic system 300 may be coupled incommunication with each other directly and/or indirectly through a bus308. The electronic system 300 may further comprise a battery 309. Itshould be noted that the scope of the present disclosure is not limitedto embodiments necessarily having one or all the listed devices.

The processing unit 302 may comprise, for example, one or moremicroprocessors, microcontrollers and the like, according to the designpreferences. The processing unit 302 may comprise, for example, one ormore processors, controllers and the like.

The memory devices 303 may comprise volatile memory devices andnon-volatile memory devices of various kinds, for example SRAM and/orDRAM memories for the volatile-type and solid state memories, magneticdisks and/or optical disks for the non-volatile-type.

Finally, it is apparent that modifications and variations may be made tothe microelectromechanical gyroscope and to the method described,without departing from the scope of the present disclosure, as definedin the attached claims.

A microelectromechanical gyroscope may be summarized as including asupport structure (6; 106; 206); a sensing mass (3; 103; 203), coupledto the support structure (6; 106; 206) with degrees of freedom along adriving direction (DD; DD′; DD″) and a sensing direction (DS; DS′; DS″)perpendicular to each other; a calibration structure (5; 105; 205)facing the sensing mass (3; 103; 203) and separated from the sensingmass (3; 103; 203) by a gap (21; 121; 221) having an average width (W;W′; W″), the calibration structure (5; 105; 205) being movable withrespect to the sensing mass (3; 103; 203) so that displacements of thecalibration structure (5; 105; 205) cause variations in the averagewidth (W; W′; W″) of the gap (21; 121; 221); a calibration actuator (20,30; 120, 30; 220, 30) configured to control a relative position of thecalibration structure (5; 105; 205) with respect to the sensing mass (3;103; 203) and the average width (W; W′; W″) of the gap (21; 121; 221).

The calibration actuator (20, 30; 120, 30; 220, 30) may include acalibration electrode (20; 120; 220), arranged on the support structure(6; 106; 206) and capacitively coupled to the calibration structure (5;105; 205), and a bias source (30) coupled to the calibration electrode(20; 120; 220).

The driving direction (DD) may be parallel to a face (6 a) of thesupport structure (6) and the sensing direction (DS) may beperpendicular to the face (6 a) and to the driving direction (DD) andthe calibration structure (5) may be connected to a fulcrum (15) fixedto the support structure (6) and may be rotatable around a fulcrum axis(F) parallel to the face (6 a) and perpendicular to both the drivingdirection (DD) and the sensing direction (DS).

The calibration structure (5) may include a calibration plate (17)coupled to the fulcrum (15) and may have a first portion (17 a) and asecond portion (17 b) opposite with respect to the fulcrum (15); thefirst portion (17 a) faces the sensing mass (3) on one side of thesensing mass (3) opposite to the support structure (6) and may beseparated from the sensing mass (3) by the gap (21).

The calibration structure (5) may include a coupling mass (18) rigidlyjoined to the second portion (17 b) of the calibration plate (17) andcapacitively coupled to the calibration electrode (20).

The gyroscope may include at least one sensing electrode (13) arrangedon the face (6 a) of the support structure (6) and facing andcapacitively coupled to the sensing mass (3) and wherein the sensingmass (3) may be arranged between the sensing electrode (13) and thecalibration structure (5) along the sensing direction (DS).

The driving direction (DD′; DD″) and the sensing direction (DS′; DS″)may both be parallel to a face (106 a; 206 a) of the support structure(106; 206 a).

The calibration structure (105; 206) may have a first side (105 a; 205a) facing one side of the sensing mass (103; 203) and separated from thesensing mass (103; 203) by the gap (121; 221) and the calibrationelectrode (120; 220) faces a second side (105 b; 205 b) of thecalibration structure (105; 205) opposite to the first side (105 a; 205a).

The calibration structure (105; 205) may be movable with respect to thesensing mass (103; 203) along the sensing direction (DS′; DS″).

The gyroscope may include at least one sensing electrode (113; 213)fixed to the support structure (106; 206) wherein the sensing mass (103;203) may be frame-shaped and the sensing electrode (113; 213) may becapacitively coupled to a respective side of the sensing mass (103;203).

The sensing electrode (113; 213) may be arranged inside the sensing mass(102; 203).

The gyroscope may include a driving mass (201), movable with respect tothe support structure (206) along the driving direction (DD″) thesensing mass (203) may be constrained to the driving mass (201) to bedragged by the driving mass in the driving direction (DD″) and movablewith respect to the driving mass (201) along the sensing direction(DS″).

The gyroscope may include a cap (7; 107; 207) joined to the supportstructure (6; 106; 206) in a gas-tight manner to form a chamber (8; 108;208) hermetically closed between the cap (7; 107; 207) and the supportstructure (6; 106; 206) wherein the sensing mass (3; 103; 203) and thecalibration structure (5; 105; 205) may be accommodated inside thechamber (8; 108; 208).

An electronic system may be summarized as including a processing unit(402) and a gyroscope (1; 100; 200).

A method for compensating an output thermal drift in amicroelectromechanical gyroscope, the microelectromechanical gyroscopemay be summarized as including a support structure (6; 106; 206) and asensing mass (3; 103; 203), coupled to the support structure (6; 106;206) with degrees of freedom along a driving direction (DD; DD′; DD″)and a sensing direction (DS; DS′; DS″) perpendicular to each other; anda calibration structure (5; 105; 205) facing the sensing mass (3; 103;203) and separated from the sensing mass (3; 103; 203) by a gap (21;121; 221) having an average width (W; W′; W″); the method includingarranging a calibration structure (5; 105; 205) facing the sensing mass(3; 103; 203) and separated from the sensing mass (3; 103; 203) by a gap(21; 121; 221) having an average width (W; W′; W″); and moving thecalibration structure (5; 105; 205) to vary the average width (W; W′;W″) of the gap (21; 121; 221).

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A microelectromechanical gyroscope,comprising: a support structure; a sensing mass, coupled to the supportstructure with degrees of freedom along a driving direction and asensing direction, the driving direction and the sensing directionperpendicular to each other; a calibration structure facing the sensingmass and separated from the sensing mass by a gap having an averagewidth, the calibration structure being movable with respect to thesensing mass so that displacements of the calibration structure causevariations in the average width of the gap; and a calibration actuatorconfigured to control a relative position of the calibration structurewith respect to the sensing mass and the average width of the gap. 2.The gyroscope according to claim 1, wherein the calibration actuatorcomprises a calibration electrode, arranged on the support structure andcapacitively coupled to the calibration structure, and a bias sourcecoupled to the calibration electrode.
 3. The gyroscope according toclaim 2, wherein: the driving direction is parallel to a face of thesupport structure and the sensing direction is perpendicular to the faceand to the driving direction; and the calibration structure is connectedto a fulcrum fixed to the support structure and is rotatable around afulcrum axis parallel to the face and perpendicular to both the drivingdirection and the sensing direction.
 4. The gyroscope according to claim3, wherein: the calibration structure comprises a calibration platecoupled to the fulcrum and having a first portion and a second portionopposite with respect to the fulcrum; and the first portion faces thesensing mass on one side of the sensing mass opposite to the supportstructure and is separated from the sensing mass by the gap.
 5. Thegyroscope according to claim 4, wherein the calibration structurecomprises a coupling mass rigidly joined to the second portion of thecalibration plate and capacitively coupled to the calibration electrode.6. The gyroscope according to claim 3, comprising at least one sensingelectrode arranged on the face of the support structure and facing andcapacitively coupled to the sensing mass and wherein the sensing mass isarranged between the sensing electrode and the calibration structurealong the sensing direction.
 7. The gyroscope according to claim 2,wherein the driving direction and the sensing direction are bothparallel to a face of the support structure.
 8. The gyroscope accordingto claim 7, wherein the calibration structure has a first side facingone side of the sensing mass and separated from the sensing mass by thegap and wherein the calibration electrode faces a second side of thecalibration structure opposite to the first side.
 9. The gyroscopeaccording to claim 7, wherein the calibration structure is movable withrespect to the sensing mass along the sensing direction.
 10. Thegyroscope according to claim 7, comprising at least one sensingelectrode fixed to the support structure and wherein the sensing mass isframe-shaped and the sensing electrode is capacitively coupled to arespective side of the sensing mass.
 11. The gyroscope according toclaim 10, wherein the sensing electrode is arranged inside the sensingmass.
 12. The gyroscope according to claim 7, comprising a driving mass,movable with respect to the support structure along the drivingdirection and wherein the sensing mass is constrained to the drivingmass to be dragged by the driving mass in the driving direction andmovable with respect to the driving mass along the sensing direction.13. The gyroscope according to claim 1, comprising a cap joined to thesupport structure in a gas-tight manner to form a chamber hermeticallyclosed between the cap and the support structure and wherein the sensingmass and the calibration structure are accommodated inside the chamber.14. A method, comprising: compensating an output thermal drift in amicroelectromechanical gyroscope, including: arranging a calibrationstructure of the microelectromechanical gyroscope facing a sensing massand separated from the sensing mass by a gap having an average width;and moving the calibration structure to vary the average width of thegap.
 15. The method of claim 14, wherein moving the calibrationstructure to vary the average width of the gap includes rotating acalibration plate of the calibration structure in a counterclockwisedirection, rotating a first portion of the calibration plate towards asensing mass of the microelectromechanical gyroscope and rotating asecond portion of the calibration plate away from a calibrationelectrode of the microelectromechanical gyroscope.
 16. The method ofclaim 14, wherein moving the calibration structure to vary the averagewidth of the gap includes rotating a calibration plate of thecalibration structure in a clockwise direction, rotating a first portionof the calibration plate away from a sensing mass of themicroelectromechanical gyroscope and rotating a second portion of thecalibration plate towards a calibration electrode of themicroelectromechanical gyroscope.
 17. A system, comprising: amicroelectromechanical gyroscope including: a support structure having asurface; a cap coupled to the support structure; a chamber delimited bythe support structure and the cap; an anchor extending from the supportstructure into the chamber; a sensing mass coupled to the supportstructure by a plurality of flexures and overlying the surface of thesupport structure; a fulcrum coupled to an end of the anchor spacedapart from the surface of the support structure, the fulcrum having afulcrum axis; a calibration structure coupled to the fulcrum, thecalibration structure having: a calibration plate coupled to thefulcrum, the calibration plate having a first portion on a first side ofthe fulcrum axis and a second portion on a second side of the fulcrumaxis, the first portion overlapping the sensing mass; a gap extendingfrom the calibration plate to the sensing mass; and a processing unitcoupled to the microelectromechanical gyroscope.
 18. The system of claim17, wherein the microelectromechanical gyroscope further includes acalibration electrode on the surface of the support structure.
 19. Thesystem of claim 18, wherein the microelectromechanical gyroscope furtherincludes a coupling mass coupled to the second portion of thecalibration plate, and the coupling mass overlaps the calibrationelectrode.
 20. The system of claim 17, wherein the calibration plate isconfigured to rotate about the fulcrum axis in a first rotationdirection towards a first operation configuration and to rotate aboutthe fulcrum axis in a second rotation direction towards a secondoperation configuration different from the first operationconfiguration, the second rotation direction being opposite to the firstrotation direction.